Rectangular bales are able to maintain their shape by means of a series of parallel extending twine loops, provided lengthwise around the bales. Balers typically use automatic knotters by which e.g. two knots are made on every loop for binding a bale. An example of such a double knotter system for a baler is disclosed in US 2006/0012176 and in BE 2012/0697 in the name of the Applicant.
At present bale length measurements are performed using a star wheel engaging the crop material. However, the parameters of the crop material, such as density, humidity, crop type, etc, may influence the amount of slip occurring as the star wheel rotates. This may lead to inaccurate measurement results.
U.S. Pat. No. 5,988,053 in the name of the Applicant discloses a system for measuring the movement of the twines to detect a wide range of mistie conditions, such as broken or jammed strands.